The “fact” that junk food is cheaper than real food has become a reflexive part of how we explain why so many Americans are overweight, particularly those with lower incomes. I frequently read confident statements like, “when a bag of chips is cheaper than a head of broccoli …” or “it’s more affordable to feed a family of four at McDonald’s than to cook a healthy meal for them at home.”

This is just plain wrong. In fact it isn’t cheaper to eat highly processed food: a typical order for a family of four — for example, two Big Macs, a cheeseburger, six chicken McNuggets, two medium and two small fries, and two medium and two small sodas — costs, at the McDonald’s a hundred steps from where I write, about $28. (Judicious ordering of “Happy Meals” can reduce that to about $23 — and you get a few apple slices in addition to the fries!)